The “geoplugin_currencyConverter” element is the conversion rate for the currency converter base currency.
Like all calls to any of geoPlugin's web services, the default base_currency is USD ($US).
Thus, if your base currency is NOT $US, then you must add the variable base_currency=XXX to the call to geoplugin.net eg

http://www.geoplugin.net/xml.gp?base_currency=EUR

Now the geoplugin_currencyConverter element will output the exchange rate of one Euro for your visitor.